Substantially, plant fiber raw materials for papermaking include: wood fiber and grassy fiber.
The parenchyma cell in the grass fiber is high content, and interlaces poorly with the fiber. For the pulp manufactured by an existing process, it is not easily bleached, so that there is minimum value of pulp and paper making. The drain ability of rice straw pulp is poor, the strength of the paper is poor, the value of the crack length is low, the tear value is low, and the folding degree is less. So far all over the world within the scope of papermaking is the most widely used wood fiber, grass fiber with less, but with the lack of forest resources greatly, how to use straw raw material chemical pulp to produce high quality is a serious problem facing now.
The existing methods for manufacturing pulp with grass plants contain: chemical method, mechanical method, chemical and mechanical method. For the chemical method for manufacturing pulp, some components of grass fiber raw material are removed to cause the raw materials dissociation into pulp by means of chemical action in the cooking step. The cooking methods in the chemical method can be subdivided into lime method, soda method, caustic soda anthraquinone method, sulfate method, sulfite method and the like.
In the prior art, it's usually considered that grass pulp need to keep cooking and stay warm for longer time for making pulp more “soft” in order to achieve chemical pulp with high whiteness. For example, the article which is entitled “Assumption and preliminary practice for strengthening the preparation of grasses and improvement of cooking” in Hubei Institute of Technology, 1999, 14(3) mentions that the hardness of pulp K value is below 10, well up to 7-8, the pulp yield reaches more than 50%, well up to 57%, and the breaking length is more than 4000 m, well up to 7000 m above, as a result, the grass pulp has advantages such as with deep delignification, lighter color, being bleached easily, good strength, high yield in cooking. However, the pulp with high hardness, especially KMnO4 value 16-22, equivalent to kappa value 23-36, is used to produce high strength unbleached pulp and bleached pulp with whiteness of 60-70% ISO, thus can reduce energy consumption and improve the yield.
The production efficiency of continuous pulping is high. For non wood fiber, in the method for manufacturing pulp, horizontal tube continuous cooking system is selected firstly. At present, it is widely used at home and abroad in that the method is mature, convenient in control, compact in structure and short in cooking time.
Chinese patent application Publication No. CN101906729A discloses a method for continuously cooking grass raw materials, comprises the following steps: (1) preparing the grass raw materials before dipping to obtain the grass raw materials after preparing and before dipping; (2) conveying the prepared fibrous raw materials into an impregnator through a screw feeder, and adding impregnation liquid for dipping treatment, putting the prepared grass raw materials and the impregnation liquid in a digester to the digester at the same time, and then adding hot black liquor for primary cooking to obtain the primarily cooked grass raw materials; (3) adding cooking liquor to the primarily cooked grass raw materials for secondary cooking to obtain pulp of the grass raw materials. The method of the invention achieves the purpose of continuously cooking the grass raw materials with large liquor ratio, shortens cooking time, reduces energy consumption and improves uniformity of the pulp. The invention further provides cooking device used in the method.
Although this method realizes to continuously cook grass raw materials in large liquid ratio, shorten the cooking time, reduce the energy consumption and improve the uniformity of the slurry, due to the use of vertical continuous digester, the scale of production will lead to a large area of plant, resulting in higher device investment.
In view of foregoing, the invention is proposed.